It is known that sodium and potassium ions are major contaminants of semiconductor materials and devices, especially integrated circuits. These ions tend to migrate through the device material, especially under an applied bias and in the presence of moisture and halogen environments. When the ions migrate to a p-n junction, they pick up an electron and become metallic elements which deposit on the p-n junction. Accumulation of these materials cause the device to short and fail. It is particularly difficult to control the presence of sodium and potassium ions since they are abundant materials in our general living environment. For example, contamination from fingerprints, residual solder fluxes and processing salts frequently leave a residue of these alkali metal ions, and particularly, sodium ions.
Various polymeric silicone resins, such as RTV silicone elastomer has been used as an encapsulant or sealant material to protect electronic semiconductor devices from mechanical damage and temperature and humidity effects of the environment. However, in the manufacturing processes employing and preparing the silicone materials used in the preparation of the elastomers, trace amounts of sodium or potassium are almost always present. When the encapsulant is employed on the electronic device, these ions tend to migrate as mentioned above, causing device failure. Consequently, a way to eliminate these contaminants or reduce their ability to migrate, especially when used as an integrated circuit encapsulant is needed. Since it is not practical to eliminate these ions from the manufacturing process of the silicones, the technique of ion trapping these contaminants has been employed.
As reported in Chemical Abstracts, March, 1976, page 39929q, Kineda et al. obtained a Japanese patent, Patent No. 76-11377, covering the use of certain macrocyclicpolyetheramines, known as cryptate ethers, in semiconductor sealing resin compositions for the purpose of acting as an alkali metal ion getter. The particular cryptate ether described in this reference is a 2,2,2 cryptate ether which is a tricyclic cryptate ether. While these cryptate ethers may effectively trap the alkali metal ions, when used in the form as described in Kineda, they ae free to migrate in the silicone polymer. This migration has two disadvantages, one being the fact that these ethers are known to have some toxicity associated with them and migration of the ether to the surface can contaminate the surface with a toxic material. In addition, migration of the ethers may allow some migration of the alkali metal ion complex therewith to the area of the p-n junction where, if the potential at the junction is high enough, it may cause the complex to breakdown resulting in deposition of the metal at the junction and shorting of the junction. I have discovered that cryptate ethers can be incorporated in the silicone resin composition so as to maintain its ability to trap the alkali metal ions but which are not free to migrate through the polymer structure.